Abstract<\/strong><\/p>\nDietary fiber is a major component of veterinary nutrition. Its effects depend on key properties such as fermentability, solubility, and viscosity, which influence gastrointestinal transit, microbiome balance, and nutrient digestibility. Fermentable fiber supports gastrointestinal health through short-chain fatty acid production, and soluble and insoluble fiber affects stool bulk and moisture. Not all types of fiber are appropriate for every condition, and inappropriate use can worsen clinical signs, especially those of megacolon or obstipation. Accurate assessment of fiber content in pet food requires evaluating total dietary fiber, not just crude fiber. By understanding fiber\u2019s multifaceted role, clinicians can tailor nutritional management strategies to meet individual patient needs and improve clinical outcomes.<\/p>\n
Take-Home Points<\/strong><\/p>\n\n- Fiber should be matched to the condition being treated; consider fermentability, solubility, and viscosity rather than using a blanket approach.<\/li>\n
- To compare diets accurately, evaluating crude fiber is not enough; when possible, evaluate total dietary fiber.<\/li>\n
- Not all patients benefit from added fiber; for patients with conditions such as obstipation or megacolon, fiber may worsen clinical signs.<\/li>\n
- Response matters more than fiber amounts; tailor fiber intake to the individual patient\u2019s tolerance and clinical response.<\/div><\/div><\/li>\n<\/ul>\n
Dietary fiber plays a valuable role in veterinary nutrition, but the term \u201cfiber\u201d is often oversimplified. Its definition can vary according to specific characteristics and how it interacts with the digestive system. Fiber is commonly used to manage conditions such as constipation, diarrhea, and anal gland irritation, among others. Depending on the type, fiber can have other attributes, such as acting as a prebiotic to support microbiome health.<\/span><\/p>\nWhen recommending fiber, consider the specific goal or intended outcome and choose a fiber type that aligns with that goal. Fiber is categorized by its fermentability, solubility, and viscosity, which influence its effect in the body. Whether evaluating a diet or adding fiber to one, these 3 properties should be matched to the condition being managed. Given the diversity of fiber properties and physiological effects, dietary fiber should be evaluated on an individual basis rather than classified broadly as universally beneficial or detrimental. Finding the right balance and selecting fiber that aligns with the patient\u2019s specific needs are essential.<\/span><\/p>\nDescription of Fiber<\/h2>\n
Fiber is the nondigestible portion of carbohydrates. Because it is not digested, fiber passes through the small and large intestines, where it can be fermented by bacteria or affect the bulk and consistency of the feces. Fiber plays a role in supporting gastrointestinal (GI) health due to its effects on the microbiome, and it is a fuel source for enterocytes; however, not all patients respond to fiber in the same way, and thus the amount and type of fiber that is fed should be considered on an individual basis. Fiber can have several effects on the GI tract, such as altering the digestibility of a diet or transit time.1<\/sup><\/span><\/p>\nCategories of Fiber<\/h2>\n
Fiber categorization is generally based on its characteristics and how it behaves in the intestinal tract. The main categories are fermentability, solubility, and viscosity (<\/strong><\/span>TABLE 1<\/span><\/strong>)<\/strong>.<\/span><\/p>\n\n\n\nTABLE 1<\/span> Type of Fiber and Its Characteristics <\/span>2,3<\/sup><\/span><\/th>\n<\/tr>\n<\/thead>\n\n\n| Type of Fiber<\/span><\/td>\n | Fermentability<\/span><\/td>\n | Solubility<\/span><\/td>\n<\/tr>\n\n| Guar gum<\/span><\/td>\n | High<\/span><\/td>\n | Soluble<\/span><\/td>\n<\/tr>\n\n| Pectin<\/span><\/td>\n | Moderate to high<\/span><\/td>\n | Soluble<\/span><\/td>\n<\/tr>\n\n| Psyllium<\/span><\/td>\n | Moderate<\/span><\/td>\n | Moderately soluble<\/span><\/td>\n<\/tr>\n\n| Flaxseed<\/span><\/td>\n | Moderate<\/span><\/td>\n | Soluble<\/span><\/td>\n<\/tr>\n\n| Beet pulp<\/span><\/td>\n | Moderate<\/span><\/td>\n | Mostly insoluble<\/span><\/td>\n<\/tr>\n\n| Hemicellulose<\/span><\/td>\n | Moderate<\/span><\/td>\n | Insoluble<\/span><\/td>\n<\/tr>\n\n| Pea fiber<\/span><\/td>\n | Moderate<\/span><\/td>\n | Insoluble<\/span><\/td>\n<\/tr>\n\n| Soybean hulls<\/span><\/td>\n | Low<\/span><\/td>\n | Insoluble<\/span><\/td>\n<\/tr>\n\n| Purified cellulose<\/span><\/td>\n | Low<\/span><\/td>\n | Insoluble<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\nFermentability<\/h3>\nFermentability refers to how easily GI bacteria can ferment a type of fiber. Fermentable fiber may produce beneficial effects in some patients but induce GI signs or intolerance in others (<\/strong><\/span>BOX 1<\/span><\/strong>)<\/strong>.<\/span><\/p>\nBOX 1 Effects of Highly Fermentable Fiber<\/div> \n \n- Speeds up gastrointestinal transit time<\/li>\n
- Reduces fecal bulk<\/li>\n
- Increases short-chain fatty acid production to support intestinal health<\/li>\n
- Can increase gas production and flatulence<\/div><\/div><\/li>\n<\/ul>\n
Fermentable fiber supports healthy bacteria within the GI tract and can help promote balance within the microbiome.4<\/sup> When fiber is fermented, bacteria produce short-chain fatty acids (SCFAs), which serve as an energy source for cells in the intestinal tract. Fermentable fibers such as inulin and fructooligosaccharides produce several SCFAs but tend to generate higher concentrations of the SCFA butyrate compared with other types of fermentable fiber. Butyrate is considered one of the preferred sources of energy for enterocytes and has been shown to promote a healthy intestinal barrier and improve water and electrolyte absorption.5<\/sup> Butyrate has also been shown to be beneficial for humans with ulcerative colitis due to its anti-inflammatory effects, which inhibit activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-\u03baB) in macrophages.6<\/sup> When NF-\u03baB is activated, it can promote inflammation; its activation has been shown to promote inflammation within the lamina propria in dogs with chronic enteropathy.7<\/sup> Using fermentable fiber to modulate inflammation in patients with chronic enteropathy is an example of how diet can be used to support intestinal health.<\/span><\/p>\nAlthough highly fermentable fiber offers many benefits, it can also increase gas production, which may lead to undesirable side effects such as intestinal distension, discomfort, and flatulence. For patients with excessive flatulence, it is helpful to review the diet ingredient list for fermentable fiber sources that may be contributing to the flatulence. Another consideration is that highly fermentable fiber can increase methane production, which may worsen signs of colitis.<\/span><\/p>\nSolubility and Viscosity<\/h3>\nFiber is also categorized by solubility (soluble or insoluble), which is associated with its viscosity as well. Viscosity refers to the ability of fiber to thicken or form a gel when mixed with liquid and has been suggested as an alternative way to describe soluble fiber.2<\/sup> Soluble fiber, or that with higher viscosity, has a greater water-holding capacity than insoluble fiber and is generally more susceptible to bacterial fermentation. However, although it may seem logical to link solubility with fermentability, the 2 properties are not always directly associated.2<\/sup> For example, beet pulp is considered an insoluble fiber, but it is also considered to be fermentable. To avoid confusion, solubility and fermentability should generally be considered separately when evaluating fiber sources (<\/strong><\/span>TABLE 1<\/span><\/strong>)<\/strong>.<\/span><\/p>\nFiber with higher viscosity can increase the water content and bulk of feces. Highly viscous fiber can also slow gastric emptying and intestinal transit time. However, the effects of fiber on transit time reported in the literature can vary depending on the study, which may be influenced by the amount of fiber used. For example, 1 study found that adding 30 g of purified cellulose to dog food slowed intestinal transit time, whereas another study found that feeding a diet containing 9% \u03b1-cellulose (as fed) resulted in faster intestinal transit time compared with that in controls.2<\/sup> It is generally accepted that soluble and viscous fiber typically delays gastric emptying and, conversely, insoluble fiber tends to speed up transit time through the small intestine and colon, meaning that contents pass more quickly; however, variations are possible.3<\/sup><\/span><\/p>\nFiber also affects digestibility. It has been shown that higher-fiber diets tend to decrease total dry matter digestibility and may influence protein digestibility as well.8,9<\/sup> Thus, therapeutic diets that are formulated to be highly digestible tend to be lower in fiber, but every diet should be examined individually as fiber variations between highly digestible diets certainly exist (<\/strong><\/span>TABLE 2<\/span><\/strong>)<\/strong>.<\/span><\/p>\n\n\n\n<\/colgroup>\n\n\nTABLE 2<\/span> Examples of Higher-Fiber Diets That Contain Limited-Ingredient or Hydrolyzed Protein<\/span><\/th>\n<\/tr>\n<\/thead>\n\n\n| Product Name<\/span>*<\/td>\n | TDF (g\/1000 kcal)<\/span><\/td>\n<\/tr>\n\nDOGS<\/span><\/td>\n<\/tr>\n\n| Royal Canin Hydrolyzed Protein, canned<\/span><\/td>\n | 57<\/span><\/td>\n<\/tr>\n\n| Purina Pro Plan Veterinary Diets HA Hydrolyzed, canned<\/span><\/td>\n | 48<\/span><\/td>\n<\/tr>\n\n| Royal Canin Selected Protein PW Moderate Calorie, dry<\/span><\/td>\n | 47<\/span><\/td>\n<\/tr>\n\n| Royal Canin Vegetarian, dry<\/span><\/td>\n | 32<\/span><\/td>\n<\/tr>\n\n| Hill\u2019s Prescription Diet z\/d, canned<\/span><\/td>\n | 27<\/span><\/td>\n<\/tr>\n\n| Hill\u2019s Prescription Diet z\/d Low Fat, canned<\/span><\/td>\n | 27<\/span><\/td>\n<\/tr>\n\n| Hill\u2019s Prescription Diet z\/d Low Fat, dry<\/span><\/td>\n | 26<\/span><\/td>\n<\/tr>\n\nCATS<\/span><\/td>\n<\/tr>\n\n| Royal Canin Gastrointestinal Hydrolyzed Protein, dry<\/span><\/td>\n | 26<\/span><\/td>\n<\/tr>\n\n| Hill\u2019s Prescription Diet d\/d (duck or venison), dry<\/span><\/td>\n | 26<\/span><\/td>\n<\/tr>\n\n| Hill\u2019s Prescription Diet d\/d (duck), canned<\/span><\/td>\n | 23<\/span><\/td>\n<\/tr>\n\nTDF=total dietary fiber.
\n*Product formulations can change over time. The fiber values presented in this chart (Purina 2025 Product Guide, purina.com<\/a>; Royal Canin Veterinary Health Nutrition Product Book May 2024, royalcanin.com<\/a>; Hill\u2019s Product Guide 2024, hillspet.com<\/a>) should be verified by using the most current product guides or by contacting the pet food<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\nFiber in Pet Food<\/h2>\nDetermining how much fiber a diet provides can be challenging. Dietary fiber is not considered an essential nutrient by AAFCO and does not have a minimum requirement. On pet food labels, fiber is reported as a maximum percentage of crude fiber. However, crude fiber mainly reflects insoluble fiber and does not indicate whether the diet contains soluble or fermentable fiber. Because of this, crude fiber can significantly underestimate total dietary fiber (TDF).<\/span><\/p>\nThe most accurate way to compare dietary fiber is to evaluate TDF <\/b>in a diet, which indicates both soluble and insoluble fiber. The AAFCO Pet Food Label Modernization initiative will eventually require that TDF be included on labels, but this will take time.10 <\/sup>TDF analysis is more involved and requires laboratories to be able to process large numbers of samples. <\/span><\/p>\nThe guaranteed analysis on labels provides percent crude fiber, which is a percentage of fiber per 100 g of food. Because this percentage is based on weight, comparing it between diets that vary in moisture and energy density is difficult. The preferred method is to compare fiber content on a caloric basis, such as grams per 1000 kcal. Grams per 1000 kcal from percent crude fiber provided on the label can be estimated as follows:<\/span><\/p>\n\n- Divide the crude fiber % by the kcal\/kg of the food.<\/li>\n
- Multiply the result by 10\u2009000.<\/li>\n<\/ul>\n
Example:<\/b> For a diet that contains 1.5% crude fiber and 3900 kcal per kg<\/span><\/p>\n\n- Step 1:<\/b> 1.5\u2009\/\u20093900\u2009=\u20090.000384<\/li>\n
- Step 2:<\/b> 0.000384\u2009<\/span>\u00d7\u200910\u2009000\u2009=\u20093.84 g crude fiber per 1000 kcal<\/li>\n<\/ul>\n
When TDF is available, comparing grams of TDF per 1000 kcal is the preferred method (<\/strong><\/span>TABLE 3<\/span><\/strong>)<\/strong>.<\/span><\/p>\n\n\n\n\n<\/colgroup>\n\n\nTABLE 3<\/span> Levels of Dietary Fiber in Dog and Cat Food3<\/sup><\/span><\/th>\n<\/tr>\n<\/thead>\n\n\n| Dietary Fiber<\/span><\/td>\n | Crude Fiber, g\/1000 kcal<\/span>*<\/td>\n | TDF, g\/1000 kcal<\/span><\/td>\n<\/tr>\n\nLow<\/span><\/td>\n<\/tr>\n\n| Dog food<\/span><\/td>\n | < 10<\/span><\/td>\n | < 20<\/span><\/td>\n<\/tr>\n\n| Cat food<\/span><\/td>\n | < 5<\/span><\/td>\n | < 5<\/span><\/td>\n<\/tr>\n\nModerate<\/span><\/td>\n<\/tr>\n\n| Dog food<\/span><\/td>\n | 10\u201320<\/span><\/td>\n | 20\u201340<\/span><\/td>\n<\/tr>\n\n| Cat food<\/span><\/td>\n | 5\u201310<\/span><\/td>\n | 10\u201325<\/span><\/td>\n<\/tr>\n\nHigh<\/span><\/td>\n<\/tr>\n\n| Dog food<\/span><\/td>\n | > 20<\/span><\/td>\n | > 40<\/span><\/td>\n<\/tr>\n\n| Cat food<\/span><\/td>\n | > 10<\/span><\/td>\n | > 25<\/span><\/td>\n<\/tr>\n\nTDF = total dietary fiber.<\/span>
\n*Crude fiber does not reflect soluble fiber within the diet, and the preferred method of comparing fiber in a diet is to evaluate the TDF. Although this table is helpful for providing general information about fiber content, always consider the amount of fiber that is in the current diet.<\/span>3<\/sup><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\nFiber for Constipated Patients<\/h2>\nIndications for Adding Fiber<\/h3>\nIf a constipated patient has normal colonic function and motility, fiber can offer several benefits that help reduce the risk for constipation. When managing constipation, the type of fiber is relevant. Soluble fiber, such as psyllium, is a viscous fiber that helps draw water into the feces, making it softer and easier to pass. Although insoluble fiber is not effective for dry, hardened feces, it can help maintain fecal bulk and stimulate colonic motility. <\/span><\/p>\nContraindications for Adding Fiber<\/h3>\nFor patients that have dry, hard feces and are unable to defecate (e.g., those with obstipation), adding fiber is contraindicated until the patient is deobstipated. For patients with megacolon, when the colon has lost its ability to contract and move feces due to poor motility, a high-fiber diet can be harmful. Adding insoluble fiber to the diet of these patients increases fecal bulk, which the colon cannot move, thereby worsening the condition. Even soluble fiber may be ineffective because the underlying issue is the inability of the colon to contract and evacuate feces. For these patients, a highly digestible, low-residue, low-fiber diet is preferred.<\/span><\/p>\nFiber for Patients with Diarrhea<\/h2>\nDiarrhea may be lessened by modifying dietary fiber, depending on the source of the diarrhea. <\/span><\/p>\n\n- Small bowel diarrhea:<\/strong> Large volume, watery, normal frequency<\/li>\n
- Large bowel diarrhea:<\/strong> Smaller volume, increased frequency, may include mucus and\/or blood, patient may exhibit straining (tenesmus)<\/li>\n<\/ul>\n
For acute small bowel diarrhea, a highly digestible diet is usually recommended as the first step. If that does not lead to a response, clinicians can explore therapeutic diets containing novel or hydrolyzed proteins. If there is still no response, it may be appropriate to trial a higher-fiber diet. Large bowel diarrhea often responds well to a higher-fiber diet; for these patients, it can be helpful to begin by increasing the fiber in the diet. If that is unsuccessful, considering a highly digestible, novel or hydrolyzed diet is often a next step in addition to increasing the fiber. <\/span><\/p>\nAlthough it is still appropriate to consider dietary fiber supplementation for either type of diarrhea, taking a methodical approach to management with fiber can help the clinician determine the best next step. Before deciding to modify the fiber in the diet, the amount of fiber in the current diet must be considered. When managing chronic enteropathy in dogs or cats, evaluating the TDF content of the diet can be helpful. Many hydrolyzed or limited-ingredient diets are relatively low in fiber, although exceptions exist. If a patient has not responded to a diet trial for diarrhea and the current diet is low in fiber, a higher-fiber limited-ingredient or hydrolyzed protein diet may be beneficial (<\/strong><\/span>TABLE 2<\/span><\/strong>)<\/strong>.<\/span><\/p>\nComorbidities and Fiber<\/h2>\nWhen managing patients with comorbidities, evaluating the fiber content of the diet is particularly valuable. A diet that provides the appropriate nutrient profile for a patient\u2019s medical condition(s) may not contain the amount or type of fiber needed to address concurrent GI concerns. <\/span><\/p>\nFor example, a cat with fiber-responsive diarrhea and renal disease may require a dietary plan that includes supplemental fiber. Although it can be challenging to match the fiber content of a high-fiber diet by using supplements alone, doing so may not be necessary. Both the type and amount of fiber play roles in managing fiber-responsive diarrhea. Evaluating the TDF content of therapeutic renal diets by different pet food manufacturers can help identify formulations that are higher in fiber and may better support patients with multiple conditions (<\/strong><\/span>TABLE 4<\/span><\/strong>)<\/strong>.<\/span><\/p>\n | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |